Hi Wout,
Yes, unfortunately FileZilla decided a few years ago to go this route. It's a shame because in all other respects it is software of excellent quality. You can opt out from these "offers" while installing, but one has to be really attentive and careful.
An alternative would be WinSCP; in general, all file transfer utilities that support SFTP. We'll look into this and consider removing our endorsement of FileZilla.
Best,
Max